We reported a case of thoracic localized, mixed variant, Castleman's Disease (angiofollicular lymph node hyperplasia) with a favourable clinical course presenting with mediastinal mass, microcytic anemia, mild thrombocytosis, polyclonal hyper-gammaglobulinaemia and without symptoms. Castleman's Disease must be always considered in the differential diagnosis of solitary mediastinal masses. Transthoracic fine needle aspiration cytology is usually nondiagnostic; in fact, cytologically, Castleman's Disease can be confused with other mediastinal lymphoproliferative disorders (such as thymomas or lymphomas). The optimal therapeutic approach is unknown but a complete surgical resection is treatment of choice for localized disease.